Ultrasonic welding is an industrial technique which uses high-frequency ultrasonic acoustic vibrations that are locally applied to workpieces being held together under pressure to create a solid-state weld. It is commonly used for plastics, and especially for joining dissimilar materials. In ultrasonic welding, there are no connective bolts, nails, soldering materials, or adhesives necessary to bind the materials together. Similar to thermal processes, ultrasonic welding generates material melts to achieve molecular bonding of the layers. An advantageous difference from common heat welding is that the heat generated by ultrasonic welding is internally located in the packaging material itself rather than by conductions from the external layers to the inside sealing surfaces.
“Ultrasonic sealing” is a type of ultrasonic welding which is used in many applications specifically for sealing multiple flexible material layers, for example, thermoplastic packaging films used in the food and other industries. During the ultrasonic sealing process, the mechanical vibrations are transferred into the packaging material by the sonotrode. This takes place at a specific frequency, with a defined force and corresponding amplitude, for a specific period of time. The ultrasonic vibrations cause friction producing heat among the molecular chains at the surfaces of the layers of the packaging material. Ultrasonic sealing forms a seal between the material layers by using at least a sonotrode and an anvil. Piezoelectric transducers create ultrasonic vibrations that the sonotrode applies to the material layers to be sealed, which are held firmly between the sonotrode and anvil. The interaction of the sonotrode and the anvil applies a particular seal profile to the material layers. The tool profile of the sonotrode and/or anvil produce and shape the resulting seal by focusing the energy of the ultrasonic vibration.
However, it was realized by the inventors of the current disclosure that problems exist when sealing some materials over an area that changes in thickness or material composition, and that improvement in ultrasonic sealing tools are needed. Therefore, embodiments of the present disclosure address these and other needs and provide other important advantages.